MACROMOLECULES
MODELING STRUCTURES FROM NMR DATA
Peter R. Seidl1,2, Erika C.A.N.Chrisman1, Príscila O. Menechini3, Katia Z. Leal2, Sonia
M.C. de Menezes4
1
Departamento de Processos Orgânicos, Escola de Química, Universidade Federal do
Rio de Janeiro, Rio de Janeiro, RJ, Brazil, 2Programa de Pós-graduação em Química
Orgânica, Instituto de Química, Universidade Federal Fluminense, Niterói, RJ, Brazil,
3
Departamento de Engenharia Química, Universidade Federal Rural do Rio de Janeiro,
Seropédica, RJ, 4CENPES, PETROBRÁS, Rio de Janeiro, RJ, Brazil
The complexity of chemical entities that make up petroleum fractions poses a
serious problem for the identification of structural features that are used for modeling
their properties. A wide variety of analytical techniques has been applied to the
asphaltene constituents of different types of petroleum for this purpose. In the case of
interactions that lead to the aggregation of asphaltene molecules, it is of fundamental
importance to characterize the aromatic ring systems and locate the positions to which
saturated rings and chains are attached. NMR spectroscopy provides this type of
information. Selective excitation techniques can be used to identify different types of
aromatic and aliphatic carbons and hydrogens and their relative proportion may be
obtained by integration of certain regions of the spectrum. The carbon-hydrogen ratio
obtained from elemental analysis can then be used to obtain the degree of unsaturation.
From this data and starting from a minimum of three aromatic rings and the
corresponding number of naphtenic rings, different types of aromatic carbons are
calculated and this data is used to generate the possible asphaltene structures. Finally,
the structure that best fits the NMR data is chosen among the possible structures.